As a guy in late 20s, I'd make following addition

21. Stop giving crap about what others think about you. No matter how nice you are, you'll always have naysayers and assholes talking crap about you.

22. Travel as much as you can. Be adventurous. “Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did do. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover.”

23. Develop friendships. Ditch shittalkers and naysayers.

24. Learn to play sports/musical instruments. Don't waste time on the internet (FB, Twitter, instagram etc) or watching TV. Pick up a hobbie. Learn new language, enhance your skills.

25. Start saving (doesn't have to be a big life project).

26. Be kind to people. Love people around you - especially family. Once they're gone, they're not coming back.

27. Volunteer. Dedicate your time to improve others' lives.

28. Don't stress on fashionable/trendy goods, especially electronic gadgets. You can get a brand new cell phone by spending your entire paycheck but guess what, after a month, some new technology will have been developed. Don't pay full price on clothes. Wait for holidays. Don't buy things based on urges.

29. Read "Don't Sweat the Small Stuff: And It's All Small Stuff" - Richard Carlson.

30. Never drink and drive. It's quite easy to make a stupid decision of that sort when you're that young, but it's not really that hard to avoid making such a stupid mistake. Also, don't start/try smoking if you haven't. QUIT if you smoke! It gets harder as you get older!